US safety investigators are considering whether an over-reliance on autopilot
systems in modern aircraft has degraded human flying skills, increasing the
risk of accidents

At a two-day hearing that starts on Tuesday, the National Transportation Safety Board (NTSB) will examine if cockpit complacency caused an Asiana Airlines flight with 307 people aboard to crash land at San Francisco International Airport in July, killing three and injuring more than 180.

Asiana Flight 214 from Seoul came in too slow and too low, causing its tail to strike a seawall just short of the runway. The tail and landing gear came off, and the plane caught fire and skidded down the runway, strewing wreckage and people over a wide area.

So far there is no evidence of mechanical failure on the Boeing 777, a plane never before involved in a fatal accident. Instead, investigators have focused on the possibility that the pilots may have mishandled the aircraft's automated controls in the final minutes of flight.

Asiana has ruled out mechanical problems with the plane and has described the pilots as experienced and competent. It has offered victims initial compensation of $10,000 (£6,087) and has vowed to improve pilot training.

The three people who died in the crash were teenagers from China who were arriving in the United States for summer camp. Authorities later ruled that one of the victims died from injuries she received from being struck by a rescue vehicle. The crash has triggered numerous lawsuits against Asiana and Boeing on behalf of victims.

The accident has fueled long-simmering concerns that pilots are relying too much on computers to fly, and losing their ability to manually land a plane when needed.

"It's exactly what they should be talking about," said Robert Schapiro, a retired pilot who has flown internationally for major airlines for 30 years.

"Automation is part of what made aviation so fantastically safe. But pilots have become totally reliant on it."

The Asiana crash was the first fatal commercial airline accident in the United States since 2009, when a regional airliner operated by Colgan Air crashed in New York state.

Boeing declined to comment ahead of the NTSB hearing. Its 777 aircraft is a widely used, long-range plane that has logged nearly 5 million flights since it entered service in 1995 and holds the world record for distance by a commercial aircraft.

Part of San Francisco airport's automated landing system was out of operation at the time of the crash. The control tower told the pilots to fly a "visual approach," meaning they had to rely on other systems, visual cues and manual skills.

The NTSB's two-day agenda is filled with pilot-training and air-safety experts from Boeing, Asiana and the Federal Aviation Administration (FAA), and pilots from Boeing and Asiana, including the first pilot to ever fly the 777.

It also includes an academic researcher who has studied pilot interactions with automated cockpit controls for decades. Nadine Sarter, a professor at the University of Michigan, is also a member of an FAA working group that recently recommended 18 areas where safety could be improved, such as pilot skill and cockpit equipment design.

Autopilot systems are highly accurate and reliable, and some airlines require pilots to use them until just before landing, so that they can minimise the chance of mistakes.

But the increased complexity "sometimes results in pilot confusion and errors," the working group said in the report.

Some pilots say they are increasingly programming flight controls rather than flying the plane itself, which diminishes their feel for the aircraft, and their ability to respond when something unexpected happens.

After the July 6 crash in San Francisco, the NTSB said the pilots appeared not to notice that the plane was well below its target landing speed and was dangerously close to stalling.

The Asiana crash has been compared to the 2009 Colgan Air flight, in which the pilots did not respond properly to a stall warning as the plane slowed dangerously just before landing near Buffalo, New York. The crash killed 50 people, including one on the ground.

Days after the Asiana crash, the FAA issued new rules on flight training that stemmed from the Colgan Air accident, that increased the flying time required for co-pilots to 1,500 hours, the same as captains, up from 250 hours.

The Asiana crash has also raised questions about how pilots are paired on flights.

Lee Kang-kook, the pilot at the controls of the Asiana flight, was attempting his first landing of a Boeing 777 jet in San Francisco and his supervisor, Lee Jeong-min, was making his first flight as a trainer. It was also the first time the two pilots had flown together, the NTSB has said.

A third pilot, part of a relief crew, was in a jump seat behind them. The fourth pilot, also part of the relief crew, was in the cabin.

According to the NTSB investigation, the pilots did not react when the plane slowed below the target landing speed of 137 knots (158 miles per hour) as it approached the runway, speed essential to keeping the jet aloft.

With less than a minute left in the flight, and the plane less than 1,000 feet off the ground, the speed slipped below 137 knots. Moments later, at just 103 knots, the pilots tried to abort the landing. But the plane was too close to the ground and struck the sea wall.